1. Field of the Invention
The present invention relates to a light-controlling element and a method for manufacturing the same.
2. Description of the Related Art
It is conventionally known to perform light control and color development by controlling the amount of light transmission or light scattering properties by using a polymer gel material (a stimulus-responsive polymer gel) which undergoes a reversible volume change (swelling/shrinking) due to a pH change, an ion intensity change, absorption or discharge of chemical material, a solvent composition change, or the provision of a stimulus such as heat, light, or electricity.
As examples of the techniques to control the amount of light transmission or light scattering properties without using any dye, Japanese Patent Application Laid-open (JP-A) Nos. 61-151621 and 62-925 disclose elements which carries out display by controlling light scattering properties by changing the difference in refractive index between a polymer gel which absorbs or discharges liquid due to a temperature change and a solvent, by the swelling and shrinking of the polymer gel.
In addition, JP-A No. 4-134325 suggests an element which carries out display by a change in the light scattering properties of a polymer gel which absorbs or discharges liquid due to an electrical stimulus. JP-A No. 7-95172 proposes an element which carries out display by changing the light scattering properties of a polymer gel through a pH change due to the ion doping and dedoping of a conductive polymer contained in the polymer gel. JP-A No. 5-188354 proposes an element which conducts a whitened or transparent display by shielding, reflecting, or scattering light or controlling a light transmitting condition by the swelling and shrinking of a polymer gel which absorbs or discharges liquid due to the action of an electric field.
On the other hand, as an example of the technique to control color developing conditions by using a dye, JP-A No. 61-149926 proposes a light-controlling element comprising a composition containing a polymer gel which absorbs or discharges liquid due to the action of an electric field and a coloring liquid containing a pigment dispersed in the liquid. This is a technique to carry out display by moving a coloring liquid by a change in the shape of a polymer gel. JP-A Nos. 61-151625 and 62-927 propose elements which make use of a colored polymer gel that decreases its optical density when swollen and that is colored when shrunk. JP-A No. 4-274480 proposes an element that carries out display by using a polymer gel bonded with a dye and changing the volume of the polymer gel, thereby changing its optical density. Furthermore, JP-A No. 9-160081 suggests an element which makes use of a change in the shape of a polymer gel adsorbed onto the surface of pigment particulates or coloring particulates so as to produce a nearly white display when the polymer gel is swollen and to produce a display of the colors of the pigment particulates or the coloring particulates when the polymer gel is shrunk, thereby changing the hue due to a volume change in the polymer gel.
The present inventors have suggested, in JP-A No. 11-236559, a novel color developing material as a coloring material with excellent contrast. This color developing material is a composition comprising a polymer gel which swells and shrinks by absorbing or discharging liquid when a stimulus is given, and which contains a pigment having a concentration not less than the concentration of saturated absorption. When the polymer gel is shrunk, the local aggregation of the pigment decreases the efficiency of light absorption, making the composition light transmissive. On the other hand, when the polymer gel is swollen, the pigment disperses into the composition to increase the efficiency of light absorption, changing the composition to a colored state.
The present inventors have also suggested, in JP-A No. 2000-231127, a composition and light-controlling material comprising a polymer gel which swells and shrinks by absorbing or discharging liquid when a stimulus is given, and which contains a light scattering member having a concentration not less than the concentration of saturated scattering. When the polymer gel is shrunk, local aggregation of the light-scattering material decreases the efficiency of light scattering, making the composition light transmissive. On the other hand, when the polymer gel is swollen, the light scattering material disperses into the composition to increase the efficiency of light scattering, changing the composition to a whitened state.
The present inventors have further suggested a light-controlling element in which a stimulus-responsive polymer gel is fixed on a substrate in JP-A No. 2001-350163. In this structure, a stimulus-responsive polymer gel is fixed on the substrate in a single particle layer so as to have a highly occupied area, and a counter substrate is provided thereon to seal liquid which is absorbed or discharged by the stimulus-responsive polymer gel between the substrates. The result is a light-controlling element which is excellent in color developing properties or light scattering properties when the gel is swollen, and which is also excellent in contrast ratio.
The present inventors have further suggested a polymer gel composition containing a stimulus-responsive polymer gel dispersed into a separating member, and a light-controlling element using the composition in JP-A No. 11-228850. Fixing the stimulus-responsive gel in the separating member can avoid the occurrence of aggregation of the gel due to its swelling or shrinking, thereby providing a light-controlling element excellent in repeating properties. JP-A No. 2002-105344 suggests a light-controlling element with excellent transparency due to reduction in the difference in refraction index between the separating member and the stimulus-responsive polymer gel. JP-A No. 2002-105327 suggests a light-controlling element with excellent transparency due to containment of the liquid that is absorbed or discharged by the stimulus-responsive polymer gel in a holding member for fixation of the stimulus-responsive polymer gel.
However, in a case where an element having a structure in which a counter substrate is provided on a substrate on which a stimulus-responsive polymer gel is fixed and in which a liquid which is absorbed or discharged by the stimulus-responsive polymer gel is sealed between the substrates is used in a light controlling glass or display, there has been a problem in that the liquid inside is scattered around if the element is broken. Moreover, when the area of the element is increased, there are cases where the substrates are deformed by the weight of the liquid, causing bubbles to be generated inside, and thus, increasing the area of the element has been difficult.
The use of a light-controlling element provided with a stimulus-responsive polymer gel dispersed into a separating member or a holding member can prevent the inside liquid from scattering when the element is broken, and can also prevent the deformation of the element when the area of the element is increased. However, homogeneous dispersion of the stimulus-responsive polymer gel requires that a precursor solution of the separating member or the holding member have high viscosity, thereby greatly limiting usable solutions. In addition, the stimulus-responsive polymer gel being dispersed in the separating member or the holding member causes unevenness in the optical density of the cell due to unevenness in the thickness of the element. Moreover, in this structure, since the stimulus-responsive polymer gel is accumulated in multiple layers, the accumulation of the gel has sometimes caused a decrease in transmittance when the element decolored.